1. Field of Invention
This invention relates to locking universal joints, and more particularly, to an apparatus and method for locking two axes of rotation in a universal joint by the application of a single lock.
2. Description of Related Art
In the field of medicine or other industries, it is often necessary to hold an object such as a tool at a stationary location. Frequently, due to space constraints or other limitations it is not possible to affix the object to a large work surface. It is therefore necessary to use an arm or other similar type member to suspend the object. Such arms may have a single or a plurality of pivots so as to allow for the rotation of the arm about one or more axes relative to the base from which the arm projects.
While in use, it is frequently necessary to adjust or reposition the arm so as to reposition the object. Adjusting the angle of the arm may be accomplished by adjusting one or more of the axes of the arm relative to the base. A conventional method for accomplishing this readjustment is to provide an adjustable and lockable pivot for each of the axis of rotation of the joint. The user may then loosen the appropriate axis lock, adjust the angle of the arm about that axis and subsequently re-lock the axis.
A disadvantage of the conventional method as set out above is that the provision of multiple pivots for each axis of rotation for the joint often results in the axes of rotation of the joints being offset such that the axes do not intersect each other. This offset produces an arm that does not rotate about a single center point. A result of this offset is that the movement of the arm may be uneven or unpredictable as the rotation of the arm changes from one axis of rotation to another axis of rotation.
Another result of this offset is that some angular movements of the arm may result in binding of the joint. Such binding may occur when a first pivot is rotated to its maximum angle of rotation in one direction. After this point, further rotational forces are applied to the second pivot which may not allow for rotation in this direction. These rotational forces applied to the second pivot that are not in alignment with the axis of rotation of this second pivot may result in a loss of movement of this second pivot, wear or damage to the joint.
Another disadvantage of a dual-pivot type design as set out above is that a separate lock is required for each of the two pivots. Adjusting such a conventional joint therefore requires the user to first adjust the angle of the first pivot and subsequently to adjust the angle of the second pivot. Additionally, the user may be required to readjust the angle of the first pivot due to any misalignment caused in the first pivot due to the movement of the second pivot. This multiple step alignment process results in a time-consuming and potentially inaccurate alignment of the arm.
Another conventional method of providing for an adjustable joint is a ball and socket type joint. Such a ball and socket joint includes a spherical portion on the end of the arm which is received within a corresponding spherical receptacle on the surface to which the arm is to be attached. The receptacle may include an adjustable diameter so as to frictionally engage the spherical portion thereby fixing the angular position of the arm.
A disadvantage of the ball and socket type joint is the reliance on friction to engage the ball within the socket. Such reliance on friction requires that the clamping force applied to the ball by the socket be relatively large to ensure adequate locking of the joint. Furthermore, it will be appreciated by those skilled in the art that such a joint will continue to be susceptible to vibration, torque or acceleration forces applied to the arm and that such applied loads may cause the friction in the joint to fail.
A further disadvantage of the ball and socket type joint is that the socket is required to encompass at least a hemisphere of the ball. Preferably, the socket would extend past the centerline of the hemisphere so as to retain the ball within the socket. This will result in a joint of this type having a limited angle of rotation due to any projection from the ball being restricted to movement within the area of the ball not covered by the socket.
What would be desirable is a lockable universal joint that is capable of being locked into a user-selected alignment by the application of a single clamping force that securely and releasably retains the universal joint in the desired alignment.